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Long-term high temperature in conventional vanadium extraction process would cause particles to be sintered and wrapped, thus reducing extraction efficiency of vanadium. Based on the purpose of directional conversion and process intensification, this work proposed a combination of low temperature sodium roasting and high efficiency selective oxidation leaching in vanadium extraction. The investigation of the reaction mechanism suggested that the structure of vanadium slag was changed by roasting, which also caused the fracture of spinel. The addition of MnO2 promoted the directional oxidation of low-valent vanadium into high valence. It also found that Na2S2O8 could oxidize low-valent vanadium effectively in leaching. The leaching efficiency of vanadium reached 87.74% under the optimum conditions, including a roasting temperature of 650 °C, a roasting time of 2.0 h, a molar ratio of sodium-to-vanadium of 0.6, a MnO2 (roasting additive) dosage of 5 wt% and a Na2S2O8 (leaching oxidant) dosage of 5 wt%. This percentage is 7.18% higher than that of direct roasting-and-leaching under the same conditions.

In the present work, to enhance the reflection loss and change the magnetic resonance frequency of barium ferrite sintered at low temperature, different amounts of Zr ion were introduced to BaFe12O19 to substitute the Fe ion. A series of M-type barium hexaferrite samples having the nominal composition BaZrxFe(12−x)O19 (x = 0.0, 0.3, 0.6, 0.9 and 1.2) was successfully synthesized by heat treatment at a relatively low temperature (900 °C) for 2 h. In order to study the phases, morphologies and magnetic properties of the substituted barium ferrites, X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) were used. The XRD patterns indicated that all samples were single phase M-type ferrites. The SEM images showed that all samples were hexagonal-shaped particles and the average size was about 500 nm. Simultaneously, a potassium chloride additive can effectively reduce the sintering temperature of barium ferrites and their formation and morphology are apparently not affected. The VSM results demonstrated that the coercivity steeply decreased from 4772.43 Oe to 797.34 Oe when the Zr ion substitution amount increased from 0.0 to 1.2 but the saturation magnetization remained almost constant (Ms = 49.71–63.06 emu g−1). Furthermore, the complex electromagnetic parameters were collected by a vector network analyzer (VNA) and the microwave absorbing properties were calculated according to transmission theory. It was found that the reflection loss is enhanced with increasing x. The minimum reflection loss value of −30.2 dB at 16.75 GHz was observed and the bandwidth is about 2.46 GHz for the x = 1.2 sample. BaZrxFe(12−x)O19 might be a promising candidate for applications of LTCC (low-temperature co-fired ceramic) substrates for millimeter wave circulators and filters.

Deep phosphorus removal from acidic leaching solution containing vanadium is a challenging problem due to the formation of complex phosphorus compounds. This problem can be possibly solved by proposed hydrogen peroxide coupled with iron-aluminum mixed salts, in which complex phosphorus compounds can be directionally converted and removed. Under the optimal conditions (the mole ratio of Fe/Al/P at 1.25:0.40:1.00, initial pH value at 5.00, reaction time for 1 h, reaction temperature at 70℃, the mole ratio of H2O2/P of 20:1), the phosphorus removal efficiency and vanadium loss rate were 99.29 % and 5.96 %, respectively. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy were used for characterization analyses of phosphorus in the removal products. Results indicated that hydroxyl radicals (·OH) made the directional conversion of complex phosphate radicals to PO43-. Complex phosphorus compounds were eventually removed in the form of PO43-. An efficient phosphorus removal progress was obtained. The concentration of residual phosphorus in solution was only 3.7 mg/L, and the mole ratio of vanadium to phosphorus in solution changed from 18 to 2353.

In the present work, to enhance the reflection loss and change the magnetic resonance frequency of barium ferrite sintered at low temperature, different amounts of Zr ion were introduced to BaFe

Hydrometallurgical leaching process enhanced by electric field coupled with sodium persulfate was developed to improve the leaching efficiency of vanadium. A high vanadium leaching efficiency of 95.64% was achieved under the optimal conditions, including roasting temperature at 650 °C, 5 wt% sodium persulfate, current density of 1000 A/m2, leaching temperature of 60 °C, leaching time of 30 min, liquid-solid ratio of 0.5 mL/g. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the mechanism. Results indicated that the low-temperature roasting changed the phase of vanadium, while O2 produced in electric field promoted the chemical conversion and oxidation process. Meanwhile, electric field expedited the collision among the moving particles, therefore it facilitated the dissolution of wrapped vanadium. It also found that electric field and sodium persulfate had synergetical effect on oxidization of low-valent vanadium to high-valence, which made the leaching efficiency increased by 26.94%. A high selective extraction of vanadium was obtained by electro-oxidation leaching with the characteristic diffraction peak of the main phases disappeared in the XRD pattern, while leaving a residue composed primarily of silicon dioxide and iron oxide. These findings could provide guidance for utilization of vanadium slag.